Toremifene, rather than tamoxifen, might be a better option for the adjuvant endocrine therapy in CYP2D6*10T/T genotype breast cancer patients in China.

Toremifene (TOR) is a valid and safe alternative to tamoxifen (TAM) for adjuvant endocrine therapy in breast cancer patients with a metabolic pathway that differs from that of TAM. TOR might have a therapeutic advantage in certain subgroups of patients, such as Chinese women with the CYP2D6 *10 (c.100C > T) T/T genotype, who would get less benefit when receiving adjuvant TAM treatment. A total of 230 breast cancer patients who received adjuvant TAM (n = 115) or TOR (n = 115) at the National Cancer Center were analyzed. The CYP2D6 *10 genotype was not significantly associated with DFS in patients who received TOR (p = 0.737). Patients treated with TOR had a higher 5-year disease-free survival (DFS) rate than those treated with TAM (89.6% vs. 80.9%, p = 0.009). TOR treatment remained an independent prognostic marker of DFS in multivariate analysis compared with TAM (hazard ratio = 0.51; p = 0.014). For all of the 50 CYP2D6 *10 T/T genotype patients, TOR treatment group had a significantly higher 5-year DFS rate than TAM group (90.9% vs. 67.9%, p = 0.031). For the remaining 170 CYP2D6 *10 C/C or C/T genotype patients, there was no significant difference between the 5-year DFS rates of the TOR and TAM groups (89.2% vs. 85.1%, p = 0.188). The advantage of adjuvant TOR over TAM in Chinese breast cancer patients might be caused by the significant benefit obtained by the CYP2D6 *10 T/T patients, who accounted for one-fifth of the overall population. TOR might be a good option for adjuvant endocrine therapy in this subgroup of patients in China.